(1) Field of the Invention
The present invention relates to a time division multiplex communication system, and more particularly, to a time division switching network used in such a system.
(2) Description of the Prior Art
In a time division multiplex communication system, a plurality of channels are assigned to a plurality of time slots in a repetition period or a frame so that digital data signals of the channels can be transmitted through a common transmission line or a highway, as well known in the prior art. In order to exchange different channels from one another on a highway or different highways, the time division switching network is used wherein digital data signals in time slots of different channels to be exchanged are replaced with one another.
A known time division switching network used for a plurality of highways includes a plurality of time-slot shifters or time switches (which will be referred to as "T-switch") and a highway switch or space switch (which will be referred to as "S-switch"). The T-switch is for replacing digital data signals between time slots of different channels on a highway, and has a speech memory of, such as a random access memory (RAM), for temporarily storing digital data signals in time slots in each one frame on the highway. The stored digital data signals are read out in an order indicated by a central control unit so as to replace the digital data signals between time slots of different channels. The S-switch has a gate matrix circuit connected to the plurality of highways, which is also controlled by control data from the central control unit so that digital data signals are replaced between time slots of different highways.
The known time division switching network is complicated in the circuit because a plurality of speech memories are used for a plurality of highways, respectively, so that a plurality control circuits are required to control the message memories, respectively. Further, a control circuit for the gate matrix of the S-switch is also necessary.